1. Field of the Invention
The present invention pertains to a method of measuring steam quality, particularly in flow lines to heavy oil production wells and the like, using a sharp-edged orifice and injection of a measured quantity of water into the flowstream passing through the orifice.
2. Background
So-called heavy oil production from subterranean reservoirs often involves the use of steam to stimulate movement of the viscous oil into the production wells. The steam is typically supplied to individual injection wells through a network of distribution pipes or "lines" from a central steam generation facility such as an electric cogeneration plant. Accordingly, the steam quality may vary somewhat in the complex distribution system and the individual supply lines leading to the respective injection wells.
Various techniques have been proposed for measuring the quality of the steam flow to each of the injection wells. Control over steam quality is important to balance the amount of energy being injected into a particular formation in order to control oil production and the efficiency of the stimulation process. Techniques which have been developed for measuring steam quality include, for example, that disclosed in U.S. Pat. No. 4,193,290 to Sustek, Jr., et al which describes an acoustic transducer associated with an orifice. Publications entitled "Kern River Field Test of a Steam Quality Measurement Technique" by C. L. Redus, et al (Society of Petroleum Engineers Publication No. SPE 17445, 1988) and "Steam Quality and Metering" by Thomas M. Wilson, The Journal of Canadian Petroleum Technology, April-June, 1976 also discuss methods for measuring steam quality utilizing a sharp-edged orifice or so-called orifice meter.
One objective in improving methods for measuring steam quality is to utilize existing facilities, where possible. Many steam distribution systems for stimulating the production of heavy oil include, in the individual, relatively small-diameter steam flow lines to each well, an existing sharp-edged orifice together with means for measuring the pressure drop across such an orifice. With these existing systems in mind, it has been determined that it would be desirable to develop a relatively uncomplicated and inexpensive method and system for surveying relatively small-diameter steam flow lines to measure steam quality in these lines from time to time and utilize such information for better control of the stimulation of the particular heavy oil reservoir.
The system and method described in the Sustek, Jr. patent requires the use of an acoustic transducer and an installation of an orifice whose acoustic signature is known from previous tests. Moreover, the technique described in the SPE publication requires installation of an orifice plate in series with a critical flow choke in each of the lines. This technique would require retrofitting of a substantial number of existing lines which incorporate only an orifice plate. Still further, the method described in the above-referenced article in the Journal of Canadian Petroleum Technology requires the use of flow meters, again, a technique which requires installation of flow meters and nozzles into already existing facilities. The disadvantages of these approaches are thus significant in existing, large and complex steam distribution networks. However, the method of the present invention substantially overcomes the disadvantages of prior art methods and systems.